Patent GB-576336-A (GB)
Title: Improvements relating to brake control systems
IPC: B60T8/32
Filed: 1943-12-16
Abstract: 576,336. Brakes. WESTINGHOUSE BRAKE & SIGNAL CO., Ltd. (Westinghouse Air Brake Co.). Dec. 16, 1943, No. 21112. [Class 103 (i)] In a brake control apparatus wherein, when wheel slip occurs, a reduction of the degree of brake application is effected followed by a reapplication of the brake when the wheel has again accelerated, the re-application is made at a reduced degree and each succeeding re-application, following fresh wheel slip, is made at a progressively reduced degree, until the slip is finally eliminated. In Figs. 1, 2, the brake cylinders 11 of each wheel truck are supplied and vented by a decelostat valve 19 under the control of a re-application control valve 25 in circuit with a rheostat 26 arranged, in conjunction with a stepping-relay 27, to insert a step-by-step increase of resistance into the circuit. The pressure admitted to the brake cylinder pipe 80 from the pipe 17 is determined by the pressure applied to the valve 19 by a pipe 18, the latter pressure being determined by a relay valve 21 and the re-application valve 25. A brake pipe 15 and a straight air pipe 16, and a master controller (not shown) of the pressure differential switch type are provided, the arrangement being such that when the brake valve is operated to supply a given pressure to the master controller, train-wires 36, 37 are connected to a positive battery wire 39, and the magnet valve 61 is energized to connect the auxiliary reservoir 22b to the train pipe 16. When the pressure in the pipe 16 balances the pressure in the master controller, the valve 61 is de-energized and cuts off the supply to the pipe 16. The release valve 62 also is controlled by the master controller and a cut-off valve 63 prevents back-flow. A control valve, comprising a pipe bracket section 45 flanked by a service section 46 and an emergency section 47, is connected to the brake pipe 15 by a pipe 48. An emergency application vents the pipe 15 at emergency rate and actuates both sections 46, 47 to admit full pressure to a pipe 58 leading to the control space 65 of the relay valve 21. The pressure admitted to the pipes 18a, 18 from the pipes 17, 17b connected to the reservoirs 23 corresponds with the pressure in the space 65, and this pressure, modified or not by the re-application valve 25, corresponds to the effective pressure supplied by the pipe 80 to the brake cylinders 11. The pipe 80 is supplied from the pipe 17 through the decelostat valve 19 which comprises a relay valve section 19b and a magnet valve section 19c which latter, when de-energized, connects the pipe 18 to the control space 77 to ensure that the pressure in the pipe 80 corresponds to the pressure applied by the pipe 18. The magnet valve is in circuit with a pressure-actuated switch 99 which when other contacts are picked. up, as described below, energizes the valve 19c and exhausts the pipe 18 causing exhausting of of the brake cylinders 11. The relay valves 19b, 21 are similarly constructed and comprise, in the former case, a supply valve 73, a release valve 74 and a floating lever 75 pivoted on a piston 76. Pressure supplied from the pipe 18 to the space 77, beneath the piston 76, closes the valve 74 and opens the valve 73 to admit fluid from the pipe 17 to the space 78 above the piston, this space being connected to the pipe 80. When the pressure in the cylinders 11 equals the pressure in the space 77, the valve 73 closes, and when the pipe 18 and space 77 are exhausted, the valve 74 opens and correspondingly exhausts the brake cylinders 11. The means for detecting wheel slip and for effecting the brake releases and re-application at a progressively decreasing intensity, comprise a D.C. generator 28 for each wheel-axle assembly, condensers 30 normally charged by the generators, in circuit with windings a of relays 29. The contacts c, d are picked up only by the discharge current from the condensers 30 caused by an abnormal deceleration of the corresponding wheels resulting from slip. The closing of the contacts c brings a holding- winding b into operation and also closes the circuit 152, 153, 154 of the magnet valve 19c. This vents the cylinders 11 and allows the slipping wheels to accelerate rapidly. The switch 99 then opens and de-energizes the valve 19c thus stopping the venting, the contacts c, d of the relays 29 dropping out and the condensers 30 again becoming charged The brakes are re-applied and the contacts c, d remain dropped out until slipping again occurs. In this case the re-application valve 25 is in circuit with the first section of the rheostat resistance 26a which is associated with a contact arm 132 on a shaft 27a arranged to be rotated step by step in a counter-clockwise direction by pawl and ratchet means associated with a magnet winding 27d which is successively energized and deenergized in accordance with the movements of the contact d of the relay 29. An additional section of the resistance 26a is put in circuit with the valve 25 with each slipacceleration cycle until the brake pressure is reduced sufficiently to avoid slip. The stepping-relay 27 is restored to its original position, when contacts f have dropped out, by the action of a contact 27e which energizes the magnet 27d when dropped out, and de-energizes it when picked up. This causes step-by-step movements of the contact arms 27c, 26c until the arm 27c reaches the end insulated stops. Repeater relays 32, 33 having transfer contacts a, b and front and back contacts e, f maintain correct polarity irrespective of direction of movement of the wheels. Two directional relays 34, 35, the windings a of which are in series with one generator 28 and the windings b of which are in series with the other generator 28, are provided to ensure that the wheel slip detection and correction means will not fail if one of the generators fails. A pressure switch 109 closes when the pressure in the pipe 58 exceeds 5 lbs. per square inch, this switch being in circuit with the relays 32, 33, but owing to the self-holding windings, the relays do not drop out if a generator fails or if the speed falls below say, eight miles per hour, the drop out occurring when the brakes are released. In a modification, the reapplication valve comprises electro-pneumatic means for controlling the loading of a regulating spring, and the pull of the magnet opposes the pneumatic control means. An increase in magnetic force, therefore, decreases the control pressure in the pipe 18 and the stepping-relay is adapted to cut-out resistance step by step. In further modifications, the stepping-relay is replaced by a pneumatic mechanism controlling the re-application valve which is a modification of a known type of brake cylinder pressure limiting valve having a variably loaded regulating-spring. The loading on the spring, and thus the control pressure in the pipe 18, is varied automatically by a piston subject to the pressure of a reservoir connected to the auxiliary reservoir through a check valve and a cutoff valve. The cut-off valve comprises diaphragms carrying a poppet-valve, the arrangement being such that the reservoir is isolated from the auxiliary reservoir during a brake application. The reservoir is vented by a magnet valve, when wheel slip occurs, until the pressure is reduced by say 10 lbs. per square inch. This results in lighter loading of the regulating spring for the next application of the brakes Provision may be made for ensuring that the reservoir is charged only to a pressure corresponding to the degree of brake application to be effected, this arrangement obviating a series of slip cycles occurring before the brake pressure is sufficiently reduced.